This invention pertains to a chair lift in which a handicapped person sits to be lowered into a swimming pool and lifted out of the pool.
Chair lifts are well-known. Many different designs have been used. One design, shown in U.S. Pat. No. 4,221,008 "Nolan", mounts the seat on a cylinder, which moves up and down on a rod mounted in the pool. The cylinder also automatically pivots about its axis to rotate the person 90.degree. so the seat is over the deck when it is in the "up" position and over the pool when it is in the "down" position. This design requires the lift to be more than twice as long as the vertical distance of travel. In order to make the lift more compact, so that it is only slightly longer than the distance of travel, the cylinder can be fixed, and the seat can be mounted on a frame fixed to the piston rod. This provides a much more compact design, but, since the seat is hanging off of the piston rod, there are substantial cantilever forces, which require the frame and piston rod to be beefed up to support the forces that are encountered when a person is sitting on the seat. In the prior art, it is known to use rollers to reduce the cantilever forces. The rollers of the prior art can roll straight up and down, but they are not suitable when the piston rod has to pivot 90.degree.. Also, rollers are not suitable for supporting the frame against tangential forces.
The lift shown in U.S. Pat. No. 4,221,008 "Nolan" has a piston which is doughnut-shaped in order to fit outside the rod as required by that design. This greatly reduces the surface area over which the fluid acts and therefore reduces the power of a lift as compared with a lift with the same diameter cylinder using a solid circular piston.